In general, the present invention relates to an inform storage apparatus, an information storing method, a recording medium and a program. More particularly, the present invention relates to an information storage apparatus and an information storing method that are capable of reducing the power consumption of a DRAM (Dynamic Random Access Memory) and reading out data of the DRAM at a high speed, relates to a program implementing the information storing method and relates to a recording medium for storing the program.
The technology of the so-called DRAM has generally been becoming popular. The DRAM is a representative memory, which is used for temporarily storing a large amount of data and allows the data to be read out from it.
In accordance with a data storage principle of the DRAM comprising memory banks each having a plurality of cells each used for accumulating an electric charge in the same way as a capacitor, digital data is stored as an electric charge accumulated in each of the cells and whether data is stored in a cell is determined by whether an electric charge is accumulated in the cell. In accordance with a principle to read out data from a cell of a DRAM, an electric charge accumulated in the cell is read out from the cell and amplified. The amplified electric charge is read out as data.
By the way, an electric charge accumulated in a cell described above will be unavoidably all discharged if the cell""s state of being unaccessed continues. The cell""s state of being unaccessed is the cell""s state in which data stored in the cell is not read out. As a result, data stored in the cell is destroyed. In order to solve this problem, electric charge stored in all cells is read out in page units at predetermined time intervals and amplified by amplifiers before being returned back to the cells in the so-called refresh processing. A page is a column of cells in a matrix in which cells of the DRAM are arranged. By carrying out the refresh processing repeatedly at predetermined time intervals, it is possible to retain data stored in the DRAM.
Since the refresh processing described above must be carried out on all cells repeatedly at predetermined time intervals, however, there is raised a problem that much power is consumed during the refresh processing.
In addition, while the refresh processing described above is being carried out, the amplifier for reading operations is in a state of electrically recharging the cell as part of the refresh processing carried out at predetermined intervals. Thus, processing to read out data from the cell cannot probably be carried out. As a result, there is raised another problem that the processing to read out data from the cell is disturbed and the processing is therefore delayed.
In order to solve the problems described above, Japanese Patent Laid-open No. Hei 9-306164 discloses a method whereby a page is subjected to refresh processing only when a timer provided for the page indicates that the page is not accessed for a period of time longer than a predetermined period. By implementing this method, a page whose data is read out during the predetermined time interval is not subjected to refresh processing. Thus, the number of states in which read processing cannot be carried out is reduced accordingly.
It is an object of both the method whereby refresh processing is carried out at predetermined intervals and the method disclosed in Japanese Patent Laid-open No. Hei 9-306164 to carry out refresh processing for all cells of the DRAM. Thus, a cell not contributing to data recording, that is, the so-called unused cell, is also subjected to the refresh processing at fixed time intervals. That is to say, a cell naturally requiring no refresh processing is also subjected to refresh processing, which causes a problem of wastefully consumed power.
It is thus an object of the present invention to reduce the power consumption of a DRAM and increase the read speed of the DRAM by reducing a period of time in which the DRAM is subjected to refresh processing.
An information storage apparatus provided by the present invention comprises:
electric charge recharging command outputting means for outputting a command to recharge accumulated electric charges into a group of cells predetermined among a plurality of cells to the group of cells at predetermined time intervals;
operating status monitoring means for monitoring operating status of the group of cells; and
command suppressing means for preventing the command to recharge accumulated electric charges from being output by the electric charge recharging command outputting means to the predetermined group of cells in accordance with the operating status of the group of cells, which is monitored by the operating status monitoring means.
The group of cells has a size of at least a page of a memory bank.
If a plurality of memory banks exist, the group of cells has a size of at least a memory bank.
The operating status may include status in which data has been stored, status in which data has not been stored, status in which the group of cells has been de-allocated as a storage area and status in which the group of cells has been allocated as a storage area.
The command suppressing means may prevent the command to recharge accumulated electric charges from being output by the electric charge recharging command outputting means to the predetermined group of cells if the operating status of the group of cells, which is monitored by the operating status monitoring means, indicates that data has not been stored or the group of cells has been de-allocated as a storage area.
The information storage apparatus may further include read command outputting means for outputting a command to read out an electric charge stored in any of the cells and the electric charge recharging command outputting means outputs a command to recharge accumulated electric charges to the group of cells predetermined among the cells for a specific one of the predetermined time intervals only when the read command outputting means does not output a command to read out an electric charge stored in any cell included in the group of cells for the specific predetermined time interval.
An information storing method provided by the present invention includes:
an electric charge recharging command outputting step of outputting a command to recharge accumulated electric charges into a group of cells predetermined among a plurality of cells to the group of cells at predetermined time intervals;
operating status monitoring step of monitoring operating status of the group of cells; and
a command suppressing step of preventing the command to recharge accumulated electric charges from being output at the electric charge recharging command outputting step to the predetermined group of cells in accordance with the operating status of the group of cells, which is monitored at the operating status monitoring step.
The present invention provides a recording medium for storing a program including:
an electric charge recharging command output control step of controlling an issuance of a command to recharge accumulated electric charges into a group of cells predetermined among a plurality of cells to the group of cells at predetermined time intervals;
an operating status monitoring control step of controlling a monitoring of operating status of the group of cells; and
a command suppression control step of controlling a suppression of a command output in processing carried out at said electrical charge recharging command output control step to electrically recharge electric charges accumulated in said group of cells to said group of cells in accordance with said operating status of said group of cells, which is monitored in processing carried out at said operation status monitoring control step.
A program provided by the present invention executes:
an electric charge recharging command output control step of controlling an issuance of a command to recharge accumulated electric charges into a group of cells predetermined among a plurality of cells to the group of cells at predetermined time intervals;
operating status monitoring control step of controlling a monitoring of operating status of the group of cells; and
a command suppression control step of controlling a suppression of a command output in processing carried out at said electrical charge recharging command output control step to electrically recharge electric charges accumulated in said group of cells to said group of cells in accordance with said operating status of said group of cells, which is monitored in processing carried out at said operation status monitoring control step.
In accordance with the information storage apparatus, the information storing method and the program, which are provided by the present invention, a command to recharge accumulated electric charges into a group of cells predetermined among a plurality of cells to the group of cells is output at predetermined time intervals, operating status of the group of cells is monitored and the command to recharge accumulated electric charges is prevented from being output to the predetermined group of cells in accordance with the monitored operating status of the group of cells.